1. Field of the Invention
This invention relates to a cathode material composition for cathode material for manufacturing a rechargeable battery, more particularly to a cathode material composition for manufacturing a rechargeable battery including a composite compound and a conductive metal oxide. This invention also relates to a rechargeable battery including a cathode made from the cathode material prepared from the cathode material composition.
2. Description of the Related Art
Along with diversified development of electronic products, there is increasing need for portable power supplies. For example, electronic consumer products, medical devices, motorcycles, automobiles, and power tools and the like require a portable power supply for power source. For current portable power supplies, rechargeable batteries are relatively popular. Since lithium rechargeable batteries have a high ratio of volume to capacity, pollution-free and recyclable charge/discharge properties, and no memory effect, it has a great development potential in the future.
Additionally, a cathode material used for manufacturing the cathode plays an important role in the performance of the rechargeable battery. Since lithium ferrous phosphate-based compound, which has an olivine or NASICON structure, is environmentally benign, relatively stable and resourceful, and has a relatively high specific capacity, and relatively good charge/discharge cycling performance and thermostability, it has been evaluated to be a good candidate as the cathode material with greatest development potential.
However, since conductivity and lithium ion diffusion rate of lithium ferrous phosphate are relatively low, the specific capacity will decrease at a high charge/discharge rate so that use of such lithium ferrous phosphate in high current density applications is restricted.
In order to improve the conductivity of such lithium ferrous phosphate, it has been proposed to reduce particle size of lithium ferrous phosphate or add conductive material to lithium ferrous phosphate. For example, Japanese Patent Publication No. 2003-323892 (hereinafter referred to as the '892 publication) discloses a method for making a cathode material, which involves mixing lithium ferrous phosphate powders, conductive metal particles and a polar solvent in a hermetic container at a temperature ranging from 100 to 250° C. Since the method of the '892 publication is required to be conducted at a relatively high temperature and pressure, and since the activity of the conductive metal particles is relatively high, it is difficult to control operating conditions in the method of the '892 publication and hence, production cost of the method is relatively expensive.
Another approach to mix conductive material with the lithium ferrous phosphate involves addition of organic material to a reactant mixture containing lithium ferrous phosphate. For example, in a solid-phase mixing process, lithium salt, iron salt, phosphate and the organic material are mixed, and then heated. The lithium salt, iron salt, and phosphate are formed into lithium ferrous phosphate powders, while the organic material is pyrolyzed to produce alkane and alkene gases, and conductive carbonaceous materials that are scattered in the lithium ferrous phosphate powders. However, the pyrolyzed products, i.e., alkane and alkene gases, cause environmental pollution and raise environmental concerns. Accordingly, this method is not recommended.
Therefore, there is still a need in the art to provide a cathode material that can satisfy electrochemical properties and that can be produced by an economical and environmental friendly method.